It sometimes appears the fossil cornucopia buried beneath Yunnan may be inexhaustible. In a paper published recently by the journal Nature, paleontologists working in the province describe what they believe is a missing evolutionary link explaining the origin of something we all take for granted — faces.

The fossil in question is that of a 419 million year-old fish that lived during the Silurian period. Previously unknown to paleontologists, the fish has been given the name Entelognathus primordialis by researchers who unearthed it near Qujing in eastern Yunnan.

The 20-centimeter long fish belongs to the now-extinct taxonomic class Placodermi — or 'plate-skinned'. These ancient fish were characterized by panels of bony, external armor and for roughly 50 million years were some of the most successful and abundant aquatic animals on earth.

The discovery of E primordialis is significant because the specimen is the first of its class to exhibit a jaw similar to that of present-day vertebrates. Previous scientific theories held that animals with modern jaws evolved from shark-like fish with cartilaginous skeletons, which at some point diverged into two groups — modern sharks and bony fish.

he international research team that discovered E primordialis was led by Dr Min Zhu of the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences. He believes the fish represents a common ancestor to both sharks and bony fish. If proven correct, such a hypothesis would mean shark-like animals were not the first to develop modern jaws. It would also indicate sharks are younger, from an evolutionary standpoint, than previously thought.

The fossil was unearthed in 2010, but not considered to be of particular interest until it was re-examined a year later. It was then that researchers discovered they had found an intact, three-dimensional specimen that deserved further inspection.

Scientists not involved with the discovery of E primordialis are happy a more thorough investigation was undertaken. Professor of paleontology at Flinders University, John Long, characterized the find as equally important to those of Archaeopteryx and the australopithecine remains commonly referred to as Lucy.

E primordialis is another in a growing list of important evolutionary finds in Yunnan. These have included a 500 million year-old 'walking cactus' unearthed near Fuxian Lake, the remains of a giant mastodon found in Zhaotong and a possible new species of human uncovered in Jianshui last year.